Events Calendar

TITLE: Relating Microstructure and Performance of Solid Oxide Cells for Improving Performance and Mitigating Degradation

ADVISOR: Soumendra Basu ME, MSE

COMMITTEE: Uday Pal ME, MSE Srikanth Gopalan ME, MSE Emily Ryan ME, MSE

CHAIR: Jorg Werner ME, MSE

ABSTRACT: Despite the abundance of renewable energy resources, a lack of economically feasible storage solutions for addressing intermittency remains a barrier to advancing their widespread adoption. Reversible solid oxide cells, which can store hydrogen during periods of renewable energy overproduction, have demonstrated potential for grid stabilization applications given their high potential efficiencies and power densities. However, to become economically competitive, improvements to reversible solid oxide cell performance stability and lifetimes are required. This research focuses on understanding the relationship between microstructure and performance in solid oxide cells and explores avenues for mitigating electrode polarization and degradation.

Connections between microstructure and performance were first considered in Ni/YSZ symmetric cells, where the relationship between reaction site density and performance was quantified in nanocatalyst-infiltrated cells using EIS, SEM and FIB/SEM 3-D reconstruction. In Ni-infiltrated electrodes, results showed that both increased triple phase boundary density and decreased reaction rate constants contribute to lowering electrode polarization at intermediate temperatures. In electrodes infiltrated with GDC, a mixed ionic/electronic conducting material, reactions can take place on the GDC surface, greatly decreasing electrode polarization. Calculations considering the performance of baseline and GDC-infiltrated electrodes indicated that reactions take place up to 84nm from triple phase boundaries on nickel scaffold particle surfaces.

Microstructure/performance relationships were also examined in full cells tested for 500h under electrolysis or reversible conditions; the fuel and oxygen electrodes were characterized with methods including low-voltage SEM, FIB/SEM 3-D reconstruction, and TEM. In both scenarios, the oxygen electrode was shown to contribute minimally to cell degradation. In the fuel electrode, degradation was mainly precipitated by Ni coarsening and loss of active sites; however, these were mitigated during reversible testing by 9% and 8% respectively compared to electrolysis-tested cells.

Finally, strategies are discussed for mitigating long-term degradation. To further stabilize reversible full cells, GDC infiltration into the fuel electrode and adjustments to oxygen electrode phase compositions to prevent long-term decomposition are suggested. On the SOC system level, ALD spinel coatings for interconnect materials are considered. To this end, a successful ALD coating process for manganese oxide on stainless steel is discussed.